Minimally invasive devices, such as catheters, are often employed for medical procedures, including those involving mapping, ablation, dilation, and the like. In a particular situation, an ablation procedure may involve creating a series of inter-connecting or otherwise substantially continuous lesions in order to electrically isolate tissue believed to be the source of an arrhythmia. During the course of such a procedure, a physician may employ several different catheters having variations in the geometry and/or dimensions of the ablative element in order to produce the desired ablation pattern and/or continuity. Each catheter may have a unique geometry for creating a specific lesion or pattern, with the multiple catheters being sequentially removed and replaced during a designated procedure to create the desired multiple lesions constituting a pattern or continuous segment of treated tissue. In addition, a selected device may have a substantially fixed geometry or dimension for a specific application and as such, may be limited to use in situations where the fixed dimensions of the device are appropriate. However, variations in the dimensions or characteristics of physiological structures may vary from patient to patient, rendering a device with specific dimensions or fixed configuration ineffective and/or difficult to use. As such, multiple devices having a range of varying fixed dimensions may be needed to successfully perform a desired treatment. Exchanging these various devices during a procedure can cause inaccuracies or movement in the placement and location of the distal tip with respect to the tissue to be ablated, and may further add to the time required to perform the desired treatment. These potential inaccuracies and extended duration of the particular procedure, not to mention the risks of complications from repeatedly inserting and retracting devices to and from an incision site, increase the risk to the patient undergoing treatment.
In addition to the inefficiencies and risks associated with using multiple devices to perform a procedure, the efficacy of certain treatment procedures, such as those involving thermal energy transfer, may be limited by poor thermal conductivity between a device and the tissue site. To provide shorter treatment durations and increased efficacy for the particular treatment provided, it is desirable to optimize the heat transfer between the specific tissue to be treated and the cryogenic element or device. In other words, heat transfer from any tissue other than that selected for treatment, such as blood or other body fluids in or passing through the vicinity of the cryogenic element for example, should be minimized or avoided. Such thermal exchange with tissues or fluids other than that targeted for treatment can reduce the thermal exchange with the targeted tissue and also require additional “cooling power” or refrigerant flow in the case of cryogenic cooling in order to complete the desired treatment. Accordingly, heat transfer with any thermal load other than the tissue to be treated should be reduced or prevented.
Accordingly, in light of the above limitations, it would be desirable to provide a medical device in which the particular size, shape, and/or dimensions of the device may be controlled and modified during use to provide ablative patterns or treatment delivery characteristics of various shapes and continuity, without the need for additional catheters or the like having a single geometric orientation that is limited in its ability to provide multiple ablative patterns or treatment characteristics for a specific tissue region. It would also be desirable to provide an apparatus and methods of use thereof having increased heat transfer efficiency during thermal exchange procedures.